Re: [PATCH] tracing/probes: Fix MAX_TRACE_ARGS limit handling

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Sun, 29 Sep 2024 23:17:14 -0400
Mikel Rychliski <mikel@mikelr.com> wrote:

> On Sunday, September 29, 2024 7:40:18 P.M. EDT Masami Hiramatsu wrote:
> > Good catch! But this silently drop the arguments after MAX_TRACE_ARGS.
> > I rather like to reject such input with an error (-E2BIG) as below.
> > (Hmm, and I also need a new ftracetest test case for this.)
> > 
> > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> > index 39877c80d6cb..3f6654127d8c 100644
> > --- a/kernel/trace/trace_probe.c
> > +++ b/kernel/trace/trace_probe.c
> > @@ -2194,6 +2194,9 @@ int trace_probe_create(const char *raw_command, int
> > (*createfn)(int, const char if (!argv)
> >                 return -ENOMEM;
> > 
> > +       if (argc > MAX_TRACE_ARGS + 2)
> > +               return -E2BIG;
> > +
> >         if (argc)
> >                 ret = createfn(argc, (const char **)argv);
> 
> I think the logic still needs to be cleaned up in the individual probe 
> implementations (either to count consistently or remove the limit enforcement 
> there), otherwise you can get an oops with something like:
> 
> 	echo "f:testprobe copy_process" arg{1..127}=\$stack "\$arg*" > out
> 	cat out > /sys/kernel/debug/tracing/dynamic_events

Ah, good catch. Yes, the "$arg*" problem is still there.

> 
> BTF argument expansion results in >128 arguments, but we still attempt to 
> process the excess unparsed ones.

OK, can you update your version to return an error from each probe?

Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>